Abstract : The stability of Lewis acid-base adducts of diboron tetrafluoride, boron trifluoride, and boron trichloride with various bases, and acid displacement reactions of the complexes are reported. It has been confirmed that boron trichloride is a stronger Lewis acid than boron trifluoride toward representative bases with both oxygen and nitrogen donor atoms. It has been established that diboron tetrafluoride is a weaker Lewis acid than boron trifluoride. Possible reasons for this difference are discussed. Good methods for the purification of boron trifluroide and boron trichloride are presented. (Author)